(1) Technical Field
This invention is concerned with improvements to standardized mechanical interface systems used for reducing particle contamination on semiconductor substrates, and more particularly to a smart tag holder and tag cover housing used with a standardized mechanical interface and pod carrier.
(2) Description of the Prior Art
Protecting fragile objects such as, for example, a plurality of semiconductor substrates held in cassettes are further contained in a mini-environment also known as a pod, a transportable carrier. In general, a pod arrangement for isolating fragile objects from external environmental conditions is acknowledged. In such an application, a pod enclosing a cassette in a small volume of motionless, particle free space is considered the cleanest achievable surroundings for protecting the surfaces of semiconductor substrates from particulates and gases. Total isolation is provided during transport, storage and processing of these substrates.
Referring to FIG. 1, of the prior art, a process station 50 for processing semiconductor substrates is shown. A particular processing line, such as photolithography, may include any number of stations as the type of station shown in FIG. 1. The stations are designed to provide processing steps such as applying photo resist materials on substrates, mask alignment for actinic exposure of the photo resist, material deposition on the semiconductor substrates, etc.
FIG. 1 also illustrates the transportable carrier pod 20 above the workstation 50 after being removed from an engaging guide tray 53. The pod shelters a cassette 30 that holds a plurality of semiconductor substrates, the cassette is shown unloaded from the pod and in the process station 50. In practice, the pod would remain engaged in the tray until all the substrates in the cassette were processed, and the cassette put back into the pod. This illustration was done to simplify the following description.
The pod 20 is removably placed on the canopy 54 of the processing station 50. An engaging guide tray 53 aligns and seals the pod cassette port 22 disposed at the bottom of pod 20 over a canopy of the process equipment. A smart-tag 40 is affixed to pod 20 to interact with a two-way communication means mounted on the workstation. The cassette passes into the process station by way of a pass-through door 52 at the base of pod alignment tray, with door 53 on the interface ports on the canopies preserving the respective environments. Latches for the two doors are opened simultaneously so that any contaminants on the surfaces of the outer doors are trapped between the doors, accordingly, preserving the clean environments of both pod and canopy into an integrated clean space. A mechanism lowers the two doors with the cassette. Latches release the pod door and the interface port simultaneously. An elevator mechanism lowers the two doors with the cassette riding on top into the canopy-covered space. A robot picks up the cassette and places it into the cassette port within the equipment. After processing, the reverse operation is carried out.
Standardized mechanical interface (SMIF) systems including pods are provided with inventory management hardware and software that can monitor the status of semiconductor substrates between process operations. A smart tag is a major interface for the SMIF pod system. A pod identification tag is mounted to the pod. The smart tag carries an updated status of the pod's inventory and communicates with all the SMIF systems, verifying therein, sequential correctness for further processing while also communicating with an operator assigned to a particular operation. The smart tag is used as part of a distributed processing system that does not require centralized control. Instead, a tag associated with the pod can store processing data pertaining to the particular substrates, and can perform calculations necessary to properly process the substrates.
The smart tag permits mobility in work-in-progress management and lot tracking. It is the intellectual component that provides sequential processing, process control, and storage/retrieval for the product. It is battery powered, stores 192 bytes of data which includes, lot identification, status of work-in-progress, process number, work area, and a cleaning schedule. However, the smart tag, as significant as it appears, has major drawbacks causing many quality issues under daily operation and use as outlined in the following list.
1. Missing Lot: Memory loss caused by shortage of battery power. This problem manifests itself by an alarm at the SMIF arm or, by confusing the stocker storage and retrieval access. This problem may occur many times in the same workday.
2. Data failure rate: This is another side effect from battery power shortage, especially during the load/unload activities. Additionally, an out of position tag on the pod relative to the infrared reader gives false data transfer information. This problem occurs often, typically about 12 times daily for an average of 250K transfers.
3. Repair rate: This can be the most critical issue with the present tag. Many tags executed data error because of chip decay or from damage caused by physical impact.
4. Tag reject rate: The present repair and maintenance salvaged seventy percent of the tags. Because of damaged LCD or chip the remaining thirty-percent had to be scraped.
5. Pod management: One tag, one pod rule is essential for pod management. This also organizes pod cleaning. When the cleaning due date is forthcoming, each pod/cassette will be cleaned prior to wafer start.
Another disadvantage with the prior art is the lost production time when the above problems occur. Debug and repair and maintenance affects production rate.